Adobe Acrobat Pro Lizenz bereits vor Jahren gekauft, lässt sich nicht mehr aktivieren

For serial number programs you may download only if you bought direct from Adobe
-Log in to your Adobe account and click this link https://account.adobe.com/products
--IF a download is available there will be a Download button under the program name
---as always, write the serial number in a text file AND copy that text file and the
---download file(s) to an external drive (or two) to be sure you always have what you need
---since Adobe DOES sometimes remove very old downloads from their file server
-if you did not buy direct from Adobe you must find your original install
-if you have an Education or volume license you MUST use your original media
--the link for an Education or volume license download is not available at all
-if you bought a disc and don't have a drive you will need to buy an external USB drive
-if you bought and lost a CD/DVD disc Adobe does not provide a replacement
-if you bought a download from a 3rd party vendor you will need to contact that vendor

what acrobat version and what error message?

Older versions of Acrobat can no longer be activated, unfortunately.